Field of the Invention
The present invention relates to winter tires, and in particular relates to a winter tire having an excellent performance on ice.
Description of the Related Art
Conventionally, winter studded tires having a tread portion provided with metal stud pins have been proposed. Since the stud pins are designed to dig into ice, such a winter tire can increase frictional force between the ground contact surface of the tread portion and icy road. Unfortunately, conventional winter tires have a problem that stud pins may be covered with small pieces of ice (hereinafter, referred to as “ice dusts”) that had been chipped off from the icy road by the stud pins during traveling on ice. The ice dusts may lower relative heights of the respective stud pins from the ground contact surface of the tread portion, and thus some stud pins may lose ability to dig into icy road to generate sufficient frictional force.
Japanese Unexamined Patent Application Publication No. 2014-151740 discloses a winter studded tire that includes a tread portion provided with a recess having a bottom with a hole and a stud pin embedded into the hole. The recess provides a space around the stud pin to hold or catch ice dusts that had been chipped off from the surface of ice during traveling, and the ice dusts held in the recess then may be released from the recess according to rotation of the tire.
Unfortunately, the studded tire disclosed by the above publication also has a problem that the ice dusts may stay in the recess over a prolonged period of time so that the stud pin would lose ability to dig into icy road.